Process for producing crystalline 1,2-polybutadiene

ABSTRACT

1,3-Butadiene is polymerized in a hydrocarbon solvent using a catalyst system containing (A) a cobalt salt, (B1) a phosphine compound having one branched aliphatic group of 3 or more carbon atoms or one alicyclic group of 5 or more carbon atoms and two aromatic groups, and (C) an organic aluminum compound, or a catalyst system containing (A) a cobalt salt, (B) (B1) a phosphine compound having one branched aliphatic group of 3 or more carbon atoms or one alicyclic group of 5 or more carbon atoms and two aromatic groups and/or (B2) a triarylphosphine compound having three aromatic groups, (C) an organic aluminum compound and (D) an active halogen-containing compound, thereby obtaining crystalline 1,2-polybutadiene.

TECHNICAL FIELD

The present invention relates to a process for producing crystalline1,2-polybutadiene, and more particularly to a process for producing1,2-polybutadiene having a high crystallinity using a specific catalystsystem, wherein the vinyl bond content of a polymer obtained is high,and the molecular weight thereof is adjustable.

BACKGROUND ART

1,2-Polybutadiene having crystallinity has hitherto been obtained by acatalyst comprising a phosphine complex of a cobalt salt, atrialkylaluminum and water (patent document 1: JP-B-44-32425, patentdocument 2: JP-A-1-249788), a catalyst comprising a phosphine complex ofa cobalt salt and methylaluminoxane (patent document 3: JP-A-8-59733),or a catalyst comprising a cobalt salt slurry, a phosphine solution andmethylaluminoxane [non-patent document 1: Dilip C. D. Nath, TakeshiShiono and Tomiki Ikeda, Journal of Polymer Science, Vol. 40, 3086–3092(2002)].

In the catalyst systems described these, it can be known by analogy thata phosphine compound having three aromatic groups is substantiallynecessary in the production of a 1,2-polybutadiene-based polymer havinga crystallinity of 34% or more. However, when those phosphine compoundsare used, it is required to lower the polymerization temperature, whichcauses an increase in the amount of a solvent used for preventingprecipitation, and in the production of the 1,2-polybutadiene-basedpolymer obtained by an exothermic reaction, the problem of increasingenergy loss such as the necessity for higher cooling capacity to apolymerization reactor.

In the above-mentioned patent document 1 (JP-B4432425), there isdescribed an example to use diphenylethylphosphine as a phosphinecompound having one aliphatic group and two aromatic groups. However, itis described that an amorphous (that is to say, having a crystallinityof 0%) polymer is obtained when the phosphine compound is used. It isdifficult to know the production of a 1,2-polybutadiene-based polymerhaving a crystallinity of 34% or more by analogy with the category ofphosphines as specifically exemplified in the gazette concerned, that isto say, the phosphine compound having one aliphatic group and twoaromatic groups.

Further, in the catalyst systems described in these, when the phosphinecomplex of the cobalt salt is used, equipment for preparing a catalystcomponent becomes large to necessitate excessive investment, because oflow solubility of the phosphine complex in an organic solvent.Furthermore, when a cobalt chloride slurry is used, the efficiency ofcatalyst is low. It is therefore necessary to use a large amount ofcatalyst in order to obtain a polymer, which causes the problems of thecoloration of the polymer due to residual catalyst and the like.

The present invention relates to a process for producing1,2-polybutadiene having a high crystallinity using a specific catalystsystem, wherein the vinyl bond content of a polymer obtained is high,and the molecular weight thereof is adjustable.

DISCLOSURE OF THE INVENTION

The present invention relates to a process for producing crystalline1,2-polybutadiene, which is characterized in that 1,3-butadiene ispolymerized in a hydrocarbon solvent using a catalyst system comprising(A) a cobalt salt, (B1) a phosphine compound having one branchedaliphatic group of 3 or more carbon atoms or one alicyclic group of 5 ormore carbon atoms and two aromatic groups, and (C) an organic aluminumcompound (hereinafter also referred to as “production process 1”).

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a flow chart showing a preferred production process forobtaining crystalline 1,2-polybutadiene of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

(A) The cobalt salt used in the catalyst of the present invention is acobalt salt of an organic acid such as cobalt chloride, cobalt bromide,cobalt iodide, cobalt octylate, cobalt versatate or cobalt naphthenate,or the like, and a cobalt salt of an organic acid such as cobaltoctylate, cobalt versatate or cobalt naphthenate is preferred in that nohalogen atom is contained. Further, of these, cobalt octylate, cobaltversatate or cobalt naphthenate is preferred from the point of highsolubility in an organic solvent.

Further, as (B1) the above-mentioned phosphine compound having onebranched aliphatic group of 3 or more carbon atoms or one alicyclicgroup of 5 or more carbon atoms and two aromatic groups, there ispreferably used, for example, a phosphine compound having one branchedaliphatic group of 3 or more carbon atoms or one alicyclic group of 5 ormore carbon atoms and two aromatic groups such as phenyl groups, such asdiphenylcyclohexylphosphine shown in formula (1),diphenylisopropylphosphine shown in formula (2),diphenylisobutylphosphine shown in formula (3),diphenyl-t-butylphosphine shown in formula (4),diphenylcyclopentylphosphine shown in formula (5),diphenyl(4-methylcyclohexyl)phosphine shown in formula (6),diphenylcycloheptylphosphine shown in formula (7) ordiphenylcyclooctylphosphine shown in formula (8).

When this catalyst system comprising (A) the cobalt salt, (B1) thephosphine compound having one branched aliphatic group of 3 or morecarbon atoms or one alicyclic group of 5 or more carbon atoms and twoaromatic groups and (C) the organic aluminum compound is used, a mixedsystem of (A) to (C) may be used. However, it is preferred thatcomponent (C) is used in combination with a phosphine complex of acobalt salt comprising component (A) and component (B1). When thephosphine complex of the cobalt salt comprising component (A) andcomponent (B1) is used, there may be used either one previouslysynthesized, or a method of bringing (A) the cobalt salt into contactwith (B1) the phosphine compound having one branched aliphatic group of3 or more carbon atoms or one alicyclic group of 5 or more carbon atomsand two aromatic groups, in a polymerization system.

Specific examples of the phosphine complexes of the cobalt saltscomprising (A) the cobalt salt and (B1) the phosphine compound havingone branched aliphatic group of 3 or more carbon atoms or one alicyclicgroup of 5 or more carbon atoms and two aromatic groups includecobaltbis(diphenylcyclohexylphosphine) dichloride,cobaltbis(diphenylcyclohexylphosphine) dibromide,cobaltbis(diphenylisopropylphosphine) dichloride,cobaltbis(diphenylisopropylphosphine) dibromide,cobaltbis(diphenylisobutylphosphine) dichloride,cobaltbis(diphenylisobutylphosphine) dibromide,cobaltbis(diphenyl-t-butylphosphine) dichloride,cobaltbis(diphenyl-t-butylphosphine) dibromide and the like, andpreferred are cobaltbis(diphenylcyclohexylphosphine) dichloride andcobaltbis(diphenylcyclohexylphosphine) dibromide.

Further, (C) the organic aluminum compounds include methylaluminoxane ora compound obtained by bringing a trialkylaluminum into contact withwater.

Of these, as methylaluminoxane, there may be used either one previouslysynthesized or one synthesized in the polymerization system.

Besides, the above-mentioned trialkylaluminum is trimethylaluminum,triethylaluminum, triisobutylaluminum, trioctylaluminum or the like, andwater is used in an amount of 0.2 to 1.0, preferably 0.3 to 0.75, by themolar ratio based on the aluminum atom of the trialkylaluminum.

As for a contacting method of the trialkylaluminum and water, water maybe brought into contact with an inert organic solvent solution of thetrialkylaluminum, in any state of vapor, liquid and solid (ice).Further, water may be brought into contact, as a dissolved state, adispersed state or an emulsified state in an inert organic solvent, oras a gas state or a mist state where it exists in an inert gas.

In the catalyst used in production process 1 of the present invention,the use ratio of (A) the cobalt salt and (B1) the phosphine compound ispreferably 1 to 5 mol of (B1) the phosphine compound per mol of (A) thecobalt salt.

Further, the amount of the phosphine complex of the cobalt saltcomprising components (A) and (B1) used is within the range of 5,000 to150,000, preferably 10,000 to 100,000, by the molar ratio of1,3-butadiene and the cobalt atom in the phosphine complex(1,3-butadiene/Co). When 1,3-butadiene/Co (molar ratio) is less than5,000, the mechanical strength of a polymer obtained is inferior. On theother hand, exceeding 150,000 results in decreased polymerizationactivity.

Furthermore, the amount of component (C) (organic aluminum compound)used is within the range of 500 to 4,000, preferably 800 to 2,000, bythe molar ratio of 1,3-butadiene and the aluminum atom in component (C)(1,3-butadiene/Al). When 1,3-butadiene/Al (molar ratio) is less than500, it is economically disadvantageous. On the other hand, exceeding4,000 results in decreased polymerization activity. The ratio of thealuminum atom of component (C) to the cobalt atom of the phosphinecomplex of the cobalt salt comprising components (A) and (B1) (Al/Co) isusually from 5 to 300, and preferably about 7.5 to 100. When Al/Co(atomic ratio) is less than 5, polymerization activity is decreased. Onthe other hand, exceeding 300 results in economical disadvantage.

The catalyst used in production process 1 of the present invention isprepared by mixing catalyst components in an inert organic solvent inany order. Preferably, as shown in FIG. 1, (A) the cobalt salt isallowed to react with (B1) the phosphine compound in an inert organicsolvent to form the phosphine complex of the cobalt salt, then,component (C) is added thereto to prepare the catalyst of the presentinvention, and 1,3-butadiene is polymerized in a hydrocarbon solventusing this catalyst, thereby obtaining crystalline 1,2-polybutadiene.

Further, the amount of (A) the cobalt salt used is within the range of5,000 to 200,000, preferably 10,000 to 150,000, by the molar ratio ofthe 1,3-diene and the cobalt atom (1,3-diene/Co). When 1,3-diene/Co(molar ratio) is less than 5,000, the mechanical strength of a polymerobtained is inferior. On the other hand, exceeding 200,000 results indecreased polymerization activity.

Furthermore, the amount of component (C) (aluminoxane) used is withinthe range of 500 to 4,000, preferably 1,000 to 3,000, by the molar ratioof the 1,3-diene and the aluminum atom in component (C) (1,3-diene/Al).When 1,3-diene/Al (molar ratio) is less than 500, it is economicallydisadvantageous. On the other hand, exceeding 4,000 results in decreasedpolymerization activity. The ratio of the aluminum atom of component (C)to the cobalt atom of component (A) (Al/Co) is usually from 5 to 300,and preferably from about 7.5 to 100. When Al/Co (atomic ratio) is lessthan 5, polymerization activity is decreased. On the other hand,exceeding 300 results in economical disadvantage.

As the inert organic solvents used for the preparation of the catalystsin the above-mentioned production processes 1 and 2 of the presentinvention, there can be used, for example, an aromatic hydrocarbon suchas benzene, toluene or xylene, an aliphatic hydrocarbon such as butane,butene, pentane, pentene, hexane, heptane or octane, an alicyclichydrocarbon such as cyclopentane or cyclohexane, a chlorinatedhydrocarbon such as methylene chloride, 1,2-dichloroethane,1,1,1-trichloroethane, chlorobenzene, o-dichlorobenzene orp-dichlorobenzene, and a mixture thereof.

As the inert organic solvents used for the preparation of the catalysts,there are also preferably used the same solvents as the polymerizationcatalysts.

Further, the catalyst may be prepared by previously mixing respectivecomponents before it is brought into contact with 1,3-butadiene of thepresent invention, or can also be prepared by mixing respectivecomponents in the presence of a conjugated diene in a polymerizationreactor.

In the present invention, 1,2-polybutadiene having a crystallinity of 5%to 40% can be produced by polymerizing 1,3-butadiene in the hydrocarbonsolvent using the catalyst system mainly comprising components (A), (B1)and (C).

In the present invention, a conjugated diene other than 1,3-butadienecan also be used together in an amount of about 10% by weight or less.The conjugated dienes other than 1,3-butadiene, which are used in thepresent invention, include a 4-alkyl-substituted-1,3-butadiene, a2-alkyl-substituted-1,3-butadiene and the like. Of these, the4-alkyl-substituted-1,3-butadienes include 1,3-pentadiene,1,3-hexadiene, 1,3-heptadiene, 1,3-octadiene, 1,3-nonadiene,1,3-decadiene and the like. Further, typical examples of the2-alkyl-substituted-1,3-butadienes include 2-methyl-1,3-butadiene(isoprene), 2-ethyl-1,3-butadiene, 2-propyl-1,3-butadiene,2-isopropyl-1,3-butadiene, 2-butyl-1,3-butadiene,2-isobutyl-1,3-butadiene, 2-amyl-1,3-butadiene, 2-isoamyl-1,3-butadiene,2-hexyl-1,3-butadiene, 2-cyclohexyl-1,3-butadiene,2-isohexyl-1,3-butadiene, 2-heptyl-1,3-butadiene,2-isoheptyl-1,3-butadiene, 2-octyl-1,3-butadiene,2-iso-octyl1,3-butadiene and the like. Of these conjugated dienes,preferred examples of the conjugated dienes used as a mixture with1,3-butadiene include isoprene and 1,3-pentadiene.

The hydrocarbon solvents used as the polymerization solvents include,for example, an aromatic hydrocarbon such as benzene, toluene or xylene,an aliphatic hydrocarbon such as butane, butene, pentane, pentene,hexane, heptane or octane, an alicyclic hydrocarbon such as cyclopentaneor cyclohexane, a chlorinated hydrocarbon such as methylene chloride,1,2-dichloroethane, 1,1,1-trichloroethane, chlorobenzene,o-dichlorobenzene or p-dichlorobenzene, and a mixture thereof. Preferredexamples thereof include cyclohexane, heptane, toluene, methylenechloride and the like. More preferred is a non-halogen hydrocarbonsolvent such as cyclohexane, heptane or toluene, from the standpoint ofthe non-halogen series.

The polymerization temperature is usually from −20° C. to +120° C., andpreferably from +10° C. to +90° C. The polymerization reaction may beconducted by either a batch system or a continuous system. The monomerconcentration in the solvent is usually from 5 to 80% by weight, andpreferably from 8 to 40% by weight.

Further, in order to produce a polymer, it is necessary that attentionis taken to avoid contamination with a compound having inactivatingaction, such as oxygen, water or carbon dioxide, to the utmost in thepolymerization system for preventing inactivation of the catalyst andthe polymer of the present invention.

When the polymerization reaction has proceeded to a desired stage, apolymerization terminator such as an alcohol, an antioxidant, anantiaging agent, an ultraviolet ray absorber and the like are added to areaction mixture, and then, a polymer formed according to an usualmethod is separated, washed and dried to be able to obtain desired1,2-polybutadiene.

1,2-Polybutadiene obtained by the production process of the presentinvention has a vinyl bond content of 85% or more, preferably 90% ormore.

Further, the crystallinity of 1,2-polybutadiene obtained by the presentinvention is preferably from 5 to 40%, and more preferably from 10 to35%. Less than 5% results in inferior mechanical strength, whereasexceeding 40% results in inferior processability. The crystallinity isadjustable by the polymerization temperature or the like.

Furthermore, the molecular weight of 1,2-polybutadiene obtained by thepresent invention is usually from 100,000 to 600,000, by the weightaverage molecular weight in terms of polystyrene. Less than 100,000results in inferior strength, whereas exceeding 600,000 results ininferior processability. The molecular weight is adjustable by thealuminum atom/cobalt atom ratio.

The halogen atom content in 1,2-polybutadiene of the present inventionthus obtained is preferably low from the standpoint of environmentalproblems, and is 200 ppm or less, more preferably 100 ppm or less andparticularly preferably 50 ppm or less. Exceeding 200 ppm results in anincrease in the amount of endocrine disrupter corresponding materialsgenerated in burning in some cases.

Here, the halogen atom content of the resulting polymer can be easilyadjusted to 200 ppm or less by using a non-halogen cobalt salt in thecatalyst system, particularly in component (B1) or component (B), and byusing the above-mentioned non-halogen hydrocarbon solvent as the solventfor catalyst preparation or the polymerization solvent.

Crystalline 1,2-polybutadiene obtained by the present invention isblended as a raw resin or raw rubber, either alone or as a mixture withanother synthetic resin, synthetic rubber or natural rubber, further,oil extended with a process oil as needed, and then, ordinarycompounding agents for vulcanized rubber such as a filler such as carbonblack, a vulcanizing agent and a vulcanization accelerator are added toperform vulcanization as a rubber composition, thereby being able to usefor applications requiring mechanical characteristics and wearresistance, for example, tires, hoses, belts, sponges, footwearmaterials, sheets, films, tubes, packaging materials, resin modifiers,photosensitive materials and other various industrial goods.

EXAMPLES

The present invention will be illustrated in greater detail withreference to the following examples, but the invention should not beconstrued as being limited by the following examples, as long as it doesnot exceed a gist thereof.

In the examples, parts and percentages are on a weight basis, unlessotherwise specified.

Further, various measurements in the examples were made in accordancewith the following methods.

The vinyl bond content (1,2-bond content) of 1,2-polybutadiene wasdetermined by an infrared absorption spectrum method (the Morero'smethod).

The crystallinity of 1,2-polybutadiene was converted from the densitymeasured by an underwater substitution method, taking the density of1,2-polybutadiene at a crystallinity of 0% as 0.889 g/cm³, and thedensity of 1,2-polybutadiene at a crystallinity of 100% as 0.963 g/cm³.

The weight average molecular weight (Mw) was measured by gel permeationchromatography (GPC) at 40° C. using tetrahydrofuran as a solvent.

The halogen atom content was determined by a fluorescent X-raymeasurement (FP method).

The melt flow index (MI) showed the amount (g) of a resin flowed out fora period of time corresponding to 10 minutes under conditions of atemperature of 150° C. and a load of 2.16 kilograms, with a melt flowindexer.

Example 1

Preparation of Cobaltbis(diphenylcyclohexylphosphine)

Dichloride Solution:

In an atmosphere of dry nitrogen, 2.2 g of anhydrous cobalt chloride,8.0 g of diphenylcyclohexylphosphine and 125 g of methylene chloridewere added into a 300-ml pressure bottle, and stirred in a constanttemperature water bath of 35° C. for 4 hours, followed by separation ofa precipitate to obtain an 8% methylene chloride solution ofcobaltbis(diphenylcyclohexylphosphine) dichloride. This solution wasdiluted with methylene chloride, and used as a 0.4% solution.

Polymerization of 1,3-Butadiene:

In an atmosphere of dry nitrogen, 25 g of 1,3-butadiene (BD) and 125 gof cyclohexane were put into a 300-ml pressure bottle, and the 0.4%solution of cobaltbis (diphenylcyclohexylphosphine) dichloride obtainedabove and a 1% (as Al atoms) solution of methylaluminoxane in toluenewere each added so as to give BD/Co (molar ratio)=30,000 and Al/Co(atomic ratio)=20, respectively, followed by polymerization in aconstant temperature water bath of 50° C. for 120 minutes.

Reaction termination was performed by adding a small amount of ethanolas a terminator.

Then, 2,6-di-t-butyl-p-cresol was added in an amount of 0.3 part basedon 100 parts of the polymer, and heated on a hot plate to remove thesolvents, thereby obtaining the polymer. The degree of polymerizationconversion was determined from the yield. Further, the halogen contentin the polymer was measured. The results are shown in Table 1.

Examples 2 to 7

Using the same technique as with Example 1, by cobalt salts andphosphine compounds shown in Table 1, solutions of phosphine complexesof the cobalt salts were prepared, and polymerization of 1,3-butadienewas conducted under conditions of BD/Co ratios and Al/Co ratios shown inTable 1. The results are shown in Table 1.

Comparative Examples 1 to 4

Using the same technique as with Example 1, by cobalt salts andphosphine compounds shown in Table 1, solutions of phosphine complexesof the cobalt salts were prepared, and polymerization of 1,3-butadienewas conducted under conditions of BD/Co ratios and Al/Co ratios shown inTable 1. The results are shown in Table 2.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Example 7 Polymerization Cyclo- Cyclo- Cyclo- Cyclo- Cyclo- Cyclo-Cyclo- Solvent hexane hexane hexane hexane hexane hexane hexaneSolvent/1,3-Buta- 5 5 5 5 5 5 5 diene (Weight Ratio) Cobalt Salt CobaltCobalt Cobalt Cobalt Cobalt Cobalt Cobalt Chloride Chloride ChlorideBromide Chloride Chloride Chloride Phosphine Compound Diphenyl DiphenylDiphenyl Diphenyl Diphenyl- Diphenyl- Diphenyl- cyclo- cyclo- cyclo-cyclo- iso- isobutyl- t-butyl- hexyl- hexyl- hexyl- hexyl- propyl-phosphine phos- phos- phos- phos- phos- phosphine phine phine phinephine phine Polymerization 50° C. 50° C. 50° C. 50° C. 50° C. 50° C. 50°C. Temperature Polymerization 120 min 120 min 120 min 120 min 120 min120 min 120 min Time BD/Co (Molar Ratio) 30,000 45,000 60,000 90,00045,000 60,000 60,000 Al/Co (Atomic 20 30 40 60 30 40 40 Ratio) Degree ofPoly- 82% 80% 80% 81% 81% 82% 78% merization Conver- sion State ofSolution Uniform Uniform Uniform Uniform Uniform Uniform Uniform VinylBond Content 95% 95% 95% 94% 94% 91% 92% Crystallinity 37% 37% 37% 36%36% 34% 34% Weight Average 150,000 170,000 230,000 140,000 160,000180,000 170,000 Molecular Weight Halogen Content 45 ppm 36 ppm 27 ppm 40ppm 35 ppm 28 ppm 30 ppm

TABLE 2 Compara- Compara- Compara- Compara- tive tive tive tive Example1 Example 2 Example 3 Example 4 Polymerization Cyclo- Cyclo- Cyclo-Cyclo- Solvent hexane hexane hexane hexane Solvent/1,3-Buta- 5 5 5 5diene (Weight Ratio) Cobalt Salt Cobalt Cobalt Cobalt Cobalt ChlorideChloride Bromide Bromide Phosphine Com- Tris(3,5- Tris(3,5- Tris(3,5-Tris(3,5- pound dimethyl- dimethyl- dimethyl- dimethyl- phenyl)-phenyl)- phenyl)- phenyl)- phosphine phosphine phosphine phosphinePolymerization 50° C. 30° C. 50° C. 30° C. Temperature Polymerization120 min 180 min 120 min 180 min Time BD/Co (Molar 60,000 60,000 90,00090,000 Ratio) Al/Co (Atomic 40 40 60 60 Ratio) Degree of Poly- 80% 78%81% 79% merization Con- version State of Solution Uniform Precipi-Uniform Precipi- tated tated Vinyl Bond Content 92% 94% 92% 94%Crystallinity 25% 35% 24% 35% Weight Average 190,000 220,000 210,000250,000 Molecular Weight Halogen Content 28 ppm 28 ppm 39 ppm 42 ppm

As apparent from Tables 1 and 2, it turns out that the polymers having ahigh crystallinity can be obtained at a polymerization temperature of50° C. in Examples 1 to 7, but that the polymerization temperature mustbe lowered to 30° C. in Comparative Examples 1 to 4, in order to obtainan equivalent crystallinity. Consequently, Examples 1 to 7 require ashorter polymerization time, but Comparative Examples 2 and 4 require alonger polymerization time, which practically causes a problem.

Example 8

Preparation of Phosphine Complex Solution:

Using the same technique as with Example 1, by a cobalt salt and aphosphine compound shown in Table 3, a solution of a phosphine complexof the cobalt salt was prepared.

Polymerization of 1,3-Butadiene:

In an atmosphere of dry nitrogen, 25 g of 1,3-butadiene (BD) and 250 gof methylene chloride were put into a 300-ml pressure bottle, and waterin the system was adjusted to water/Al (molar ratio)=0.7. In a statecooled to 10° C., an 8% solution of triisobutylaluminum in methylenechloride was added so as to give BD/Co (molar ratio)=20,000 and Al/Co(atomic ratio)=20, followed by thorough stirring. Then, the resultingsolution of the phosphine complex of the cobalt salt was added so as togive BD/Co (molar ratio)=20,000, and thereafter, the bottle wasimmediately placed in a constant temperature water bath of 20° C.,followed by polymerization for 60 minutes.

Reaction termination was performed by adding a small amount of ethanolas a terminator. Then, 2,6-di-t-butyl-p-cresol was added in an amount of0.3 part based on 100 parts of the polymer, and heated on a hot plate toremove the solvents, thereby obtaining the polymer. The degree ofpolymerization conversion was determined from the yield. The results areshown in Table 3.

Comparative Examples 5 to 7

Using the same technique as with Example 8, by cobalt salts andphosphine compounds shown in Table 3, solutions of phosphine complexesof the cobalt salts were prepared, and polymerization of 1,3-butadienewas conducted under conditions of BD/Co ratios and Al/Co ratios shown inTable 3. The results are shown in Table 3.

TABLE 3 Compara- Compara- Compara- tive tive tive Example 8 Example 5Example 6 Example 7 Polymerization Methylene Methylene MethyleneMethylene Solvent Chloride Chloride Chloride Chloride Solvent/1,3-Buta-10 10 10 10 diene (Weight Ratio) Cobalt Salt Cobalt Cobalt Cobalt CobaltBromide Bromide Bromide Bromide Phosphine Com- Diphenyl- Tris(3,5-Tris(3,5- Tris(3,5- pound cyclohexyl dimethyl- dimethyl- dimethyl-phosphine phenyl)- phenyl)- phenyl)- phosphine phosphine phoshinePolymerization 20° C. 20° C. −5° C. 20° C. Temperature Polymerization 60min 60 min 90 min 60 min Time BD/Co (Molar 20,000 20,000 15,000 20,000Ratio) Al/Co (Atomic 20 20 15 20 Ratio) Degree of Poly- 86% 81% 83% 84%merization Con- version State of Solution Uniform Uniform Precipi-Uniform tated Vinyl Bond Content 95% 92% 95% 93% Crystallinity 38% 29%37% 30% Weight Average 160,000 170,000 180,000 160,000 Molecular WeightHalogen Content 351 ppm 387 ppm 524 ppm 483 ppm

As apparent from Table 3, it turns out that the polymer having a highcrystallinity has been obtained at a polymerization temperature of 20°C. in Example 8, but that the polymers having a low crystallinity havebeen obtained at a polymerization temperature of 20° C. in ComparativeExamples 5 and 7. On the other hand, it turns out that thepolymerization temperature must be lowered to −5° C. in ComparativeExample 6, in order to obtain an equivalent crystallinity. Consequently,Example 8 requires a shorter polymerization time, but ComparativeExample 6 requires a longer polymerization time, which practicallycauses a problem.

As described above, in a method which can be known by analogy from thedescriptions of JP-B-44-32425, JP-A-1-249788 and JP-A-8-59733, that isto say, in a case that a phosphine compound having three aromatic groupsis used as the phosphine compound, a lower crystallinity is obtainedunder equivalent conditions. When it is intended to obtain a polymerhaving an equivalent crystallinity, the polymerization temperature mustbe lowered, which causes an increase in the amount of a solvent used forpreventing precipitation, and in the production of the 1,2-polybutadieneobtained by an exothermic reaction, the problem of increasing energyloss such as the necessity for higher cooling capacity to apolymerization reactor. It is therefore apparent that the method isindustrially disadvantageous.

INDUSTRIAL APPLICABILITY

Crystalline 1,2-polybutadiene obtained by the present invention isblended as a raw resin or raw rubber, either alone or as a mixture withanother synthetic resin, synthetic rubber or natural rubber, further,oil extended with a process oil as needed, and then, ordinarycompounding agents for vulcanized rubber such as a filler such as carbonblack, a vulcanizing agent and a vulcanization accelerator are added toperform vulcanization as a rubber composition, thereby being able to usefor applications requiring mechanical characteristics and wearresistance, for example, tires, hoses, belts, sponges, footwearmaterials, sheets, films, tubes, packaging materials, resin modifiers,photosensitive materials and other various industrial goods.

1. A process for producing crystalline 1,2-polybutadiene, comprisingpolymerizing 1,3-butadiene in a hydrocarbon solvent with a catalystsystem comprising (A) a cobalt salt, (B1) a phosphine compound havingone branched aliphatic group of 3 or more carbon atoms or one alicyclicgroup of 5 or more carbon atoms and two aromatic groups, and (C) anorganic aluminum compound.
 2. The process for producing crystalline1,2-polybutadiene according to claim 1, wherein the catalyst systemcomprises a phosphine complex of a cobalt salt obtained by mixingcomponent (A) and component (B1), and component (C).
 3. The process forproducing crystalline 1,2-polybutadiene according to claim 1, whereincomponent (A) is at least one selected from the group consisting ofcobalt chloride, cobalt bromide, cobalt octylate, cobalt versatate andcobalt naphthenate.
 4. The process for producing crystalline1,2-polybutadiene according to claim 1, wherein component (B1) isdiphenylcyclohexylphosphine.
 5. The process for producing crystalline1,2-polybutadiene according to claim 1, wherein the use ratio ofcomponent (B1) to mol of component (A) is from 1 to 5 mol.
 6. Theprocess for producing crystalline 1,2-polybutadiene according to claim1, wherein the amount of component (C) is within the range of 500 to4,000 by the molar ratio of 1,3-butadiene and the aluminum atom incomponent (C) (1,3-butadiene/Al).
 7. The process for producingcrystalline 1,2-polybutadiene according to claim 1, wherein thehydrocarbon solvent is selected from the group consisting of cyclohexanemethylene chloride and mixtures thereof.
 8. The process for producingcrystalline 1,2-polybutadiene according to claim 1, wherein thepolymerization temperature is from −20° C. to +120° C.
 9. The processfor producing crystalline 1,2-polybutadiene according to claim 1,wherein the crystallinity of the resulting 1,2-polybutadiene is from 5to 40%.